A. Field of the Invention
This invention relates to improvements in staple spinning processes and, particularly, to improvements in ring spinning processes. The term "strand" when used herein refers to a bundle of staple fibers (natural fibers or lengths cut from filaments) having little or no bundle twist, such as slivers and rovings. The term staple yarn when used herein refers to yarn consisting of staple fibers bound together by twist. In staple spinning processes strands are normally drafted and twisted to provided staple yarns.
B. Description of the Prior Art
In the carpet industry nylon strands (e.g. slivers) are converted to staple yarns on ring spinning frames. A typical frame consists of a plurality of spinning positions each having a drafting system for drafting a strand to a desired count, a rotatable spindle for inserting twist (i.e. spindle twist) in the strand, a pigtail, and a ring-and-traveler take-up mechanism for collecting the twisted strand (staple yarn) on a bobbin mounted on the spindle. The pigtail guide is positioned directly above the centerline of the major axis of the spindle to facilitate collection of the yarn on the bobbin.
Usually, the productivity of spinning frames is maximized by operating the spindles at their maximum mechanically practical speed and then correlating the peripheral speed of the front rolls (delivery speed) to insert just enough spindle twist in the strand to provide twist at the nip of the front rolls. (Increasing the delivery speed reduces spindle twist and causes the twist in the strand to move away from the nip toward the spindle.) In the absence of twist in the strand, individual fibers flare outwardly from the surface of the strand, lick back around the front rolls and pull the strand apart causing breaks or "ends down". With twist in the strand at the nip, breaks usually occur at thin spots in the strand (i.e. imperfections) while the twisted strand is in the balloon and under a relatively high tension (balloon tension). Under normal operating conditions, 30 to 40 ends down per 1000 spindle hours is considered to be acceptable performance.
One disadvantage of operating spinning frames under the conditions described above is that a high level of twist must be inserted in the strand to provide twist in the strand at the nip of the front rolls--much more twist than is needed or even desirable for carpet end use applications, for example, bulked continuous filament (BCF) yarn contains less twist than corresponding staple yarn and, as a result, has more "apparent value", that is, less ounces of BCF yarn are needed per square yard of carpeting to achieve a carpet of the same body.
The twist level of staple yarn can be reduced while still providing twist at the nip of the front rolls by slowing down the spindle speed. However, slowing down the spindle speed, reduces productivity. U.S. Pat. No. 2,590,374 shows inserting a mechanical false twister on a ring spinning frame downstream of the front rolls. With this arrangement it is possible to increase the delivery speed somewhat and reduce the twist level in the yarn while still providing twist at the nip of the front rolls. (The twister inserts twist in the strand which backs up the strand into the nip of the front rolls.) However, as the deliver speed is gradually increased, the frequency of breaks in the balloon increases until, finally, a speed is reached at which the strand lacks sufficient strength to withstand the balloon tension and the process cannot be run. The observed twist inserted in the strand by the mechanical false twister does not pass through the twister into the balloon. Therefore, as the deliver speed is increased and the spindle twist level reduced, the strength of the strand in the balloon is reduced and even slight imperfections in the strand that were masked with twist under normal operating conditions are now a problem with respect to breaks.